[ticket/11620] Minor changes to tests for coding standards

PHPBB3-11620
[ticket/11620] Rename provider -> mock_auth_provider

Rename the class and file name to better match
what the class is mocking, as well as implement the
interface of that class.

PHPBB3-11620
[ticket/11620] Removed unnecessary lines and whitespace

PHPBB3-11620
[ticket/11620] Added a test for unset_admin

PHPBB3-11620
[ticket/11620] Abstracted session setUp into a test_case class

When defining a database test case with a setUp function, it is important
to call the parent's setup function, because that is when the database is setup.

PHPBB3-11620
[ticket/11620] Refactored unset_admin_test to use testable_facade

PHPBB3-11620
[ticket/11620] Added manual key test

PHPBB3-11620
[ticket/11620] Added a session key reset test

PHPBB3-11620
[ticket/11620] Typo in file name session_key_tests -> test

PHPBB3-11620
[ticket/11620] Remove typo in beginning of session_key_test

PHPBB3-11620
[ticket/11620] Added a test for checking if users are banned

PHPBB3-11620
[ticket/11615]  Rename continue -> check_isvalid for clarity

PHPBB3-11615
[ticket/11615] Refactored isvalid test to be more imperative

Refactoring the continue/is_valid test to remove
the confusing data provider work around, while
still keeping redundancies down to a minimum.

PHPBB3-11615
[ticket/11620]  Refactored check_isvalid_test to use session_test_case

Since the continue->isvalid refactoring is now in a branch with the
session_test_case framework, this test can be refactored to use that framework.

PHPBB3-11620
[ticket/11620] Fixed a typo on check_ban_test

PHPBB3-11620
[ticket/11620] Fixed check_ban_test errors with cache and ban warning message

PHPBB3-11620
[ticket/11620] Added garbage_collection_test

PHPBB3-11620
Merge branch 'feature/session-storage' of github.com:asperous/phpbb3 into feature/session-storage